With vehicle architectures rapidly undergoing fundamental changes towards zone-based architecture, brake systems are becoming increasingly intelligent to meet the future needs and requirements of automated driving, electrification and digitalisation.
Till now, in most series production vehicles, the braking system is somewhat like this. There’s a brake pedal that’s connected physically to the hydraulic master cylinder which in turn is connected to a pushrod that exerts force on the piston(s) in the cylinder, causing fluid from the brake fluid reservoir to flow into a pressure chamber through a compensating port. Pressurised fluid reaches each wheel through a piped set-up. The vehicle could be using drum or disc brakes or a combination. Usually in a disc brake set-up, there’s an additional brake booster. The advantage is that it uses half of the applied pedal pressure to create the same amount of brake pressure as conventional vacuum booster brakes. In a nutshell, there many components involved in the set-up and it can get complicated depending on the vehicle type.
Since conventional braking systems use a lot of fluid, safety issues have been raised from time to time when the Hydraulic Electronic Control Unit (HECU) in the vehicles may malfunction due to an electrical short or component failure, resulting in a brake fluid leak. Cars with an Anti-Lock Brake System (ABS) module may leak brake fluid internally and cause an electrical short and a possible fire hazard.
With each generation, cars are getting more advanced with connected features and a high level of digitalisation. Several braking system makers have realised this aspect and have developed future braking systems that can be applied to both ICE and EVs. The system being promoted is called the dry braking system and several tech companies have showcased the working concept and its benefits.
What is a dry braking system?
In a dry brake system, as the name implies, brake fluid is not required. In this system, brake pressure is therefore not generated by the pressure of fluids in the hydraulic system, instead actuator driven electric motors are used.
The key advantage of the dry braking system is that it is a compact unit and doesn’t need any elaborate plumbing. The other advantage is that it can be used stand alone or in combination with the conventional hydraulic set-up.
The idea of this concept has been well accepted and Continental has planned for series production with a North American car manufacturer 2025.
Continental’s Future Brake System uses electromechanical brakes on the rear axle which are operated dry, without brake fluid. On the front axle, the wheel brakes continue to be operated hydraulically. The new technology also includes the second-generation brake-by-wire system MK C2.
FBS roadmap
Continental will be introducing a technology change at its customer from wet to a semi-dry-brake system. On the front axle the wheel brakes continue to be operated hydraulically, whereas it is operated dry on the rear axle . The new technology also includes the second-generation brake-by-wire system MK C2.
The FBS gives the car manufacturer the freedom to go to a smart actuator hardware where the software can be distributed on any electronic control unit to ensure safety redundancy and offering flexibility to car makers — especially those that are leaning towards developing software-defined vehicles.
Ranging from FBS 0 to FBS 3, Continental’s roadmap shows the evolution of brake controls to motion systems and draws the path towards completely dry brakes at the rear and front axles. At the beginning of this roadmap (FBS 0) is the award-winning, second generation of Continental’s brake-by-wire system MK C2 brake system, as the gateway into all Future Brake Systems.
In the next development step (FBS 1), it is no longer necessary to mount the system directly at a specific location on the firewall in front of the driver to enable mechanical fallback. Instead, an electronic pedal supports new vehicle concepts involving different vehicle interiors and dimensions, such as the skateboard chassis of electrified vehicles on which various bodies can be mounted. With FBS 2, the brake system starts to become “dry on one axle” and with FBS 3, the brake system can be broken up into modules — wherein the hydraulic system could be entirely removed.
Another tech player ZF has showcased an electro-mechanical brake system where braking force is generated at each wheel by an electric motor, similar in approach like that of the other tech developer. Interestingly, even though there is no longer a mechanical connection between the brake pedal and the brake actuators, the braking feel is the same as that of a hydraulic brake.
Key advantages of FBS
Compared with conventional braking systems, the new brake-by-wire system, like Integrated Brake Control (IBC), enables shorter braking distances and better recovery of braking energy. There are significant performance benefits as well. For instance, during an automatic emergency braking situation, the braking distance at a speed of 100 km/h can be up to nine metres shorter than with conventional braking systems. What’s more, EVs can achieve up to 17 percent more range via even better recuperation of braking energy.
With dry brake-by-wire systems in particular, the residual drag torques that occur with conventional braking systems due to minimal contact between the brake pads and the brake discs can be reduced to almost zero. This results in even fewer particulate emissions due to brake abrasion. This lower resistance during driving also saves energy and can increase range in an EV.
Dispensing with a hydraulic system means significantly lower assembly and logistics costs even during vehicle production, as the system consists of fewer parts. And during the vehicle’s service life, the user benefits because brake fluids no longer need to be changed, reducing the amount of servicing required in the workshop.
The safety of the data transmission and processing as well as the energy supply to the electric motors is ensured by the duplication of all connections and systems, as is also common in by-wire systems in aviation.
The way forward
ZF claims that it has one of the most comprehensive portfolios of purely electronically controlled steering, brakes or damping systems for software-defined vehicles. The company says that purely electronically controlled and networked by-wire systems offer better vehicle control, shorter braking distances, more steering flexibility, greater driving stability at high speeds, and greater range and efficiency.
This feature was first published in Autocar Professional’s January 1, 2024 issue.